The present invention relates to a load-unload system and method for transferring printed circuit boards (P.C.B.'s) to a processing device, such as an inserter for mounting electronic components on a printed wiring board or a tester for testing a function of the circuit of a printed circuit board provided with electronic components.
"Printed circuit board" in this specification includes both a printed wiring board on which electric or electronic components are to be mounted and a printed circuit board on which electric or electronic components are already mentioned for formation of a circuit thereon.
In the production of printed circuit boards, the printed circuit boards are housed in a magazine for conveyance from one process to a subsequent process so as to facilitate handling and to protect the boards. During some processes, a load-unload system draws the printed circuit boards from the magazine and supplies them to a processing device. After the processing of the printed circuit boards, the boards are discharged from the device and placed in the same or another magazine by the load-unload system.
There are two known kinds of printed circuit board load-unload systems. One is a pass-through-type in which the printed circuit boards discharged from the processing device are transferred to a new magazine. The other is a return-type in which the printed circuit boards discharged from the processing device are returned to the original magazine. The return-type is better than the pass-through-type from the standpoint of the installation space requirements of the system, since the latter requires space for stocking empty magazines for receiving printed circuit boards discharged from the processing device, in addition to space for stocking magazines housing printed circuit boards to be processed by the device.
A return-type, load-unload system according to the prior art includes a magazine stocker unit, in which a plurality of magazines are arranged on a conveyor unit, and a load-unload unit, by which printed circuit boards housed in each magazine are fed to a processing device in series, one after another, and returned to each magazine after processing.
The prior art return-type, load-unload system, however, is complicated in construction and the efficiency of supplying the printed circuit boards to the processing device is low.
Also, the load-unload unit of the prior art system deals with the magazines in sequence according to the order of the arrangement in the magazine stocker unit. It cannot automatically change the sequence. Therefore, if a magazine which houses printed circuit boards different from those to be processed by the processing device is inadvertently mixed in with the magazines in the stocker unit, a human operator must stop the system and change the arrangement of the processing device so that the different magazine can be processed, or remove that magazine when it reaches the load-unload unit. When the system is operated by automatic control, the processing device is usually designed to automatically stop when such a magazine reaches the load-unload unit.
In short-run production, which has become increasingly widespread recently, a testing machine must also be able to perform a plurality of tests. Each time the printed circuit pattern is changed, new testing steps and instruments must be set in the machine. Obviously, it is best to test printed circuit boards having the same circuit pattern in series continuously. Therefore, it is desirable to arrange magazines including printed circuit boards of the same type in series. Until now, however, magazines including printed circuit boards having different patterns have been supplied to the stocker unit of the load-unload system at random. It is desirable to be able to group the magazines in the stocker unit so that the same magazines are continuously fed to the testing machine.